The present invention generally relates to fuel-fired heating appliances and, in a preferred embodiment thereof, more particularly provides a specially designed power vented, gas fired water heater having incorporated in its combustion chamber a non-flame type burner ignition system which operates at least intermittently during non-demand periods of the water heater to controllably ignite flammable vapors entering the combustion chamber through a flame arresting perforated plate structure.
Gas-fired residential and commercial water heaters are generally formed to include a vertical cylindrical water storage tank with a main gas burner disposed in a combustion chamber beneath the tank. The main burner is supplied with a fuel gas through a gas supply line, and combustion air through an air inlet flow path providing communication between the exterior of the water heater and the interior of the combustion chamber. In applications in which a sufficient natural draft is not available to draw hot combustion products upwardly through the flue portion of the water heater, to thereby transfer combustion heat to the water stored in its tank, a draft inducer fan is operatively coupled to the flue. Water heaters of this type, in which a fan is used to provide the necessary draft during water heating periods, are commonly referred to as power-vented water heaters.
Fuel fired water heaters extremely safe and quite reliable in operation. However, under certain circumstances extraneous flammable vapors from outside the water heater may enter the combustion chamber and be ignited therein. various proposals have previously been made to controllably ignite such extraneous vapors within the combustion chamber. one such proposal has been to provide an outer wall portion of the combustion chamber with flame quenching openings disposed therein and operative to permit ambient combustion air and extraneous flammable vapors to flow therethrough into the combustion chamber and be ignited, but preclude the reverse passage of flames through the flame quenching openings.
This proposed solution lends itself particularly well to gas fired water heaters operating under natural draft conditions and provided with standing pilot flames since extraneous flammable vapors entering the combustion chamber during non-demand periods of the water heater tend to be simply burned in a controlled manner by the standing pilot flame as they enter the combustion chamber.
However, the use of a standing pilot flame in a power vented gas fired water heater is not generally feasible since during non-demand periods of the water heater (in which the draft inducer fan is not operated), there is typically not sufficient natural draft present to exhaust the combustion products of a standing pilot flame. Instead, a spark igniter is typically provided in a power vented gas fired water heater and is operated, to light the main gas burner, only when a demand for water heating is present. Thus, during non-demand periods of the water heater, it may under certain circumstances be possible for extraneous flammable vapors to enter the combustion chamber through its arrestor plate flame quenching openings and accumulate in an unignited condition in the combustion chamber until a water heating demand signal is received to operate the spark igniter and light the main gas burner. The resulting ignition of the flammable vapors within the combustion chamber may undesirably tend to be more forceful than would be the case of a standing pilot flame maintained in the combustion chamber of a natural draft water heater.
in view of this, it would be desirable to provide a technique for more controllably igniting extraneous flammable vapors that may enter the combustion chamber of a power vented, fuel fired water heater during non-heating demand periods thereof. It is to this goal that the present invention is directed.
In carrying out principles of the present invention, in accordance with a preferred embodiment thereof, a power vented, fuel fired heating apparatus is provided which is representatively a gas fired water heater and comprises a combustion chamber thermally communicatable with a fluid to be heated, the combustion chamber being partially bounded by a flame arrestor portion with spaced flame quenching combustion air inlet openings therein. A fuel burner is disposed within the combustion chamber and is operable during heating demand periods of the heating apparatus, a flue is operatively communicated with the combustion chamber, and a fan is associated with the flue and is operable to create a forced draft therein during the heating demand periods of the heating apparatus.
According to a key feature of the invention, the heating apparatus also comprises ignition apparatus including a non-flame type ignition device disposed within the combustion chamber and operative at least intermittently during non-heating demand periods of the heating apparatus. In this manner, extraneous flammable vapors which may migrate into the combustion chamber via the flame quenching combustion air inlet openings in its flame arrestor portion during a non-heating demand period of the heating apparatus are ignited with a relatively soft ignition force during such non-heating demand period.
In a first illustrative embodiment of the heating apparatus, the ignition apparatus comprises a first spark igniter operative to light the fuel burner at the beginning of each heating demand period, and a second spark igniter operable intermittently (representatively at intervals of from about 15 seconds to about 30 seconds) during non-heating demand periods to provide a softened ignition for extraneous flammable vapors that might enter the combustion chamber through the flame quenching combustion air inlet openings of its flame arrestor portion.
In a second illustrative embodiment of the heating apparatus, the ignition apparatus comprises a single spark igniter which is operable at the beginning of each heating demand period to light the fuel burner, and is also operable intermittently (representatively at intervals of from about 15 seconds to about 30 seconds) during non-heating demand periods to provide a softened ignition for extraneous flammable vapors that might enter the combustion chamber through the flame quenching combustion air inlet openings of its flame arrestor portion.
In a third illustrative embodiment of the heating apparatus, the ignition apparatus comprises a spark igniter which is operable at the beginning of each heating demand period to light the fuel burner, and an auxiliary non-flame type ignition device, such as a hot surface igniter or a glow coil, which is continuously operable during non-heating demand periods to provide a softened ignition for extraneous flammable vapors that might enter the combustion chamber through the flame quenching combustion air inlet openings of its flame arrestor portion.